This is how the co - pilot locked the pilot out of the cockpit on Germanwings flight # 4U9525. [1:02]

Description:Did Germanwings co-pilot Andreas Lubitz deliberately keep his colleague out of the cockpit in order to crash Flight 4U9525 into the French Alps? A prosecutor at the heart of the investigation believes recordings indicate that the pilot who left the cockpit was prevented from getting back inside. How is it possible to keep someone out of the cockpit..(more)

Did Germanwings co-pilot Andreas Lubitz deliberately keep his colleague out of the cockpit in order to crash Flight 4U9525 into the French Alps? A prosecutor at the heart of the investigation believes recordings indicate that the pilot who left the cockpit was prevented from getting back inside. How is it possible to keep someone out of the cockpit? The BBC explains the protocol flight crew go through to enter the cabin, and how someone can be kept out.
Video footage from an Airbus promotional video